The present invention relates to a method and a device for the automatic control of illumination devices, particularly of a motor vehicle, according to the species defined in the independent claims. Such methods are already knownxe2x80x94for example, from the German Patent 195 23 262xe2x80x94but they describe only how the external illumination devices are controllable on the basis of an absolutely incident quantity of light. However, an unwanted change in the control characteristic results due to various aging effects.
The method of the present invention having the features of the main claim has the advantage that the control element, which acts on the illumination devices, is calibrated at time intervals, thereby permitting compensation for aging effects of the optical media situated in the sensing region.
A further advantage is yielded if the calibration parameters of a rain sensor, which is likewise calibrated at time intervals, are relayed to the control element. The rain sensor and the control element for controlling illumination devices are frequently arranged in a single housing and have similar or even identical optical media. The result is that the aging process of both optical media proceeds in a similar or really identical manner.
The measures specified in the dependent claims yield advantageous further developments and improvements of the features indicated in the main claim.
It is advantageous if the rain sensor has a transmitter, a receiver and a light-conducting member; the receiver receives the light conducted through the light-conducting member from the transmitter and compares this signal to a setpoint value. In this way, the transmission properties are easily ascertainable, which means a simple calibration of the control element may be carried out.
A higher accuracy may be achieved if a transmittance is determined as result from the comparison of the received light signal to the setpoint value, and the control element is calibrated with the aid of this transmittance, since it is substantially responsible for the shift of the operating point of the control element.
If the control element has a second light-conducting member which is in correlation with the optical properties of the first light-conducting member, then this correlation may be taken into account in the calibration of the control element. In this way, the light-conducting member of the control element may be different from the light-conducting member of the rain-sensor device, in particular may be made of various plastics or glasses. Due to the correlation of the optical properties, the control element may still be calibrated exactly.
If the correlation is stored as a functional cohesion in the control element, any correlation as desired of the optical properties of the two light-conducting members may advantageously be taken into account in the calibration, provided they are able to be represented functionally.
If the calibration is carried out with the aid of a correlation stored as a table in the control element, storage and computing power of the control element are minimized. The calibration can then be carried out in a very simple manner without having to forfeit some of the flexibility of the correlation.
In addition, it is particularly advantageous to provide a calibration section over which a calibration parameter, which is taken into account during the calibration, is determined at time intervals (I).
A very simple calibration may also advantageously be performed, in that it is only carried out as a function of time. Particularly in the case of plastics, it is possible to proceed in this manner as a rough approximation of the transmission change, which means no further measuring distances are necessary.
A further beneficial calibration possibility is given if the calibration is a function of the brightnesses measured during the history of the control element. The optical properties of many plastics change as a function of time and the intensity of the light to which the plastics are exposed. If these variables are measured, with the aid of empirical values, it is possible to draw conclusions about the optical properties of the plastic.
Moreover, it is advantageous to in each case construct the light-conducting members and the electronics of the rain sensor and the control element in one piece in order to save installation space and reduce costs.
The device of the present invention having the features of claim 10 has the advantage that the control element is calibrated at time intervals. It is thereby possible to compensate for aging effects of the optical media, situated in the sensing region, or of the receivers. In this context, it is particularly advantageous if the calibration parameters of a rain sensor are usable for calibrating the control element.
It is particularly advantageous if the rain sensor has a transmitter, a receiver and a light-conducting member, and the receiver receives the light conducted from the transmitter through the light-conducting member, to in this way emit transmission-dependent signals. Transmission properties are ascertained in this manner, thereby allowing a calibration of the control element. If, moreover, the control element has a second light-conducting member whose optical properties are in correlation with the light-conducting member of the rain sensor, a simple and nevertheless precise calibration of the device advantageously results.
Due to the storage of the correlation in the control element as a functional cohesion, it is possible to store every correlation of the optical properties of the two subassemblies, rain sensor and control element, representable as function.
The correlation is advantageously also stored in the control element as a cohesion in table form, in order to permit a rapid calibration using as little computing expenditure as possible.
If the two light conductors of the rain sensor and of the control element are constructed in one piece, then a similar change in the optical properties results, since both are subject to the same exposure of sunlight. This is advantageous since the transmission properties of plastics are influenced substantially by the ultraviolet radiation to which they are subject during exposure to sunlight.
In addition, arranging the electronics of the control element and the electronics of the rain sensor in one piece on a single printed-circuit board saves costs and resources.
It is also advantageous if the control element is able to be calibrated at time intervals using a calibration parameter which is a function of the service life of the control element. Aging effects of the optical media, or even aging effects of the receiver elements, which typically are constructed as semiconductor components, are to a high degree time-dependent, which means the calibration on the basis of the service life represents a good first approximation.
It is also particularly advantageous to be able to calibrate the control element with the aid of a calibration parameter which is a function of the history of the control element. Since the aging of the control element is accelerated by high irradiating light intensities, the calibration may be carried out, for example, using a calibration parameter which is calibrated from the sum of the intensities that have previously fallen on the control element and been measured.